Gear pump



April 28, 1964 M. M. MEADS 3,130,682

GEAR PUMP Filed Dec. 21, 1962 INVENTOR A TTORNEY 3,1%,682 Patented Apr. 28, 1964 "ice Delaware Fiied Dec. 21, 1962, Ser. No. 246,477

4 Claims. (Cl. 103-126) This invention relates to gear pumps, and more particularly to a housing port arrangement that eliminates back pressure between the meshing gear teeth.

Gear pumps having gears with involute gear teeth are plagued with a relatively low eiiciency. This is due 1n part to the porting arrangement of the housing and the gear to housing clearances. Housing port shapes reduce turbulence and back pressure caused by the trapping of pumped liquid between the meshing teeth of the counterrotating gears. As usually happens, the working spaces between adjacent gear teeth form dedendum pockets of decreasing volume as the opposite gear tooth enters the space, and a partial hydrostatic lock will develop unless the trapped liquid can escape. This problem has been somewhat reduced by various porting configurations. One way is to provide channels in the housing that communicate with the dedendum pockets and with the pump outlet port so that as the pockets decrease in volume, the trapped liquid is forced laterally out between the ends of the meshing teeth and through the small channels provided thus escaping through the port.

A serious disadvantage to this technique is that power is consumed by forcing the liquid through small communicating passages, but more importantly, the hydrostatic lock condition is not eliminated in all positions of gear movement. It is a purpose of the present invention to provide an improved pump of the positive displacement type having meshing involute gear teeth; to eliminate hydrostatic lock in such a pump in all gear positions; to provide a gear pump whereby the meshing gear teeth seal between the high and low pressure sides or" the pump; to provide a pump in which the pumped fluid is sucked into the dedendum pockets between the gear teeth at the earliest possible rotational position of the gears; and to provide a pump which may be operated with equal efficiency regardless of the direction of movement of the gears so that the pump may be used for pumping liquids in either direction.

This invention is accomplished by providing a gear pump of the type described including a housing having an inlet port and an outlet port; a pair of meshing gears rotatively received in the housing having involute gear teeth; a depression formed in the housing communicating with one of the ports and with a dedendum pocket between the meshing gear teeth, said depression being characterized adjacent the meshing gear teeth by a shape that conforms with the line of action of the teeth on one side and with the working circle depth thereof on the other, whereby the dedendum pocket is free to the passage of pumped uid in the connected port.

The invention will be more fully described in the following description and drawings wherein:

FIGURE l is a side view of the pump partially broken away to showthe housing interior and one gear;

FIGURE 2 is a bottom view of the gear pump shown in FIGURE l with the bottom plate removed; and

FIGURE 3 is the same as FIGURE 2 except that the gears are turned slightly from the position shown in FIG- URE 2.

Referring to the drawing, the pump includes a housing 12 of cast iron, or the like, having a central chamber 14 which may be closed by the plate 16; or if the pump is to be used as an oil pump with an internal combustion engine, the plate 16 may be omitted and the pump mounted directly to the engine block. A pair of gears 18 and Ztl are meshed and arranged for countererotation within the chamber 14 on shafts 22 and 2d journaled in the housing; at least one of the shafts being exposed to an outside source of power whereby the attached gear becomes the driving gear and the other the driven gear. When the gears are installed, the chamber 14 is divided by the partition l5 into a low pressure inlet port 30 and a high pressure outlet port 32; this designation depends on the gear 18 being rotated clockwise and the gear 20 counter-clockwise, but the pump may be operated in either direction by reversing the direction of rotation of the gears. Hereinafter it is assumed that the uid to be pumped enters at the low pressure port Sti and is carried around between the gear teeth of each counter-rotating gear and is discharged at the high pressure port 32 being then conveyed through the outlet 35.

The loss in efiiciency of positive displacement gear pumps is attributable to several factors. At least one is the percent to which the dedendum pockets between adjacent teeth of each gear are not lled on the low pressure side of the ptunp; another is the degree of back pressure created by trapped fluid when the gear teeth enter the meshing space on the high pressured side of the pump.

It is a purpose of this invention to provide a high and low pressure port configuration for a pump housing which will greatly reduce the effects on pumping eiiiciency of these factors.

In FIGURE 2, we see my pump with the bottom plate lo removed. The position of the gears is just prior to the beginning of volume increase for dedendum pocket et). By inspection it may be seen that the tooth 42 has almost completely entered the pocket 4d to the working circle depth (the circle that circumscribes the maximum distance that each tooth projects into the mating space); and it can be visualized that at, and just prior to the position shown, tooth 42 is in the process of descending into the meshing space, being pushed by tooth 44 of the driving gear 18. During this period, the teeth 42 and dit are in sliding and rolling contact along a line across the face width thereby closing any radial escape path over the top of tooth 44 into high pressure port 32. for liquid in pocket 4d. As counter-rotation continues, a partial hydrostatic lock would develop in the pocket 4Q causing a back pressure on the gears unless the trapped liquid is relieved.

For this purpose, the high and low pressure ports 3) and 32 have opposed asymmetrically shaped iinger-like depressions 46 and 4S formed in the housing wall and extending along one side of the gears into the meshing zone. These depressions are shown in FIGURE 2 by the dotted lines beginning at the working circle depth 5@ and 52, respectively, and proceeding therealong roughly to the center oi the pump adjacent partition 15. At this point, the depressions curve along the partition and veer in opposite directions coincident with the line of action of the gear teeth. The line of action is the line described by the locus of a point moving at the surface of the meshing gear teeth coincident with the line of Contact between the teeth; that locus for involute gear teeth generating a straight line. The line of action for the involute gear teeth shown can be visualized as lying in the wall portions 54 and 56 of depressions 46 and 48 respectively; passing diagonally through the partition 15.

It can be seen in FIGURE 2 that a small tip of the depression i6 registers with the near empty dedendum pocket 40 on the low pressure side. The pocket relieves any residual iluid still in pocket 453, but when tooth 42 passes the pitch point p, the pocket begins to till at this instant, being sealed from the high pressure side along the line of action by the pressure contact between gear teeth 42 and 44. lust prior to the position shown, the

pocket 40 was still registering with high pressure depression 48 hence, it is understood that the pocket will always connect with one or the other depressions at any given position in the meshing zone. As the volume of pocket 40 increases, as shown in FIGURE 3, a suction action developes which, in effect, draws fluid to be pumped from the low pressure port 30 through the depression 46 and into the expanding pocket.

Referring again to FIGURE 3, we see that the position of the gears has been changed slightly from their position in FIGURE 2. Visualizing in slow motion the intervening gear movement, the gear tooth 44 is seen gradually entering the opposite meshing space and in the process radially squeezing out high pressure fluid into the port 32. At some instant of rotation, the addendum of tooth 44 will be very close to the face of the trailing tooth 45, and except for back-lash tolerances, will virtually seal off the escape of liquid radially over the top of tooth 45. From this point, a partial hydrostatic lock is common in most gear pumps since no adequate relief is provided for the trapped liquid.

In the present invention, however, a continuous escape passage is found in the form of depression 48. Note that wall 52. of the depression follows the working circle depth throughout the trapping range and if the fluid cant escape over the top of tooth 45 it is freely pushed out the end between the meshing teeth into the depression 48 on the high pressure side 32. At the instant of rotation illustrated in FIGURE 3, the majority of the pumped uid has been dumped and only a small pocket of residual fluid remains. It may be seen by close inspection, however, that a small area or tip of the depression 48 still communicates with the dedendum pocket to relieve this iiuid as well.

Naturally, minor modifications may be made and adapted for other types of pumps and although a specific gear pump has been illustrated and described herein, it is intended that obvious changes of the illustrative embodiment be included in the scope of the appended claims, except insofar as limited by the prior art.

I claim:

1. A gear pump comprising;

a housing having an inlet and an outlet port;

a pair of meshing gears rotatably received in the housing, the gears each having involute gear teeth forming a dedendum pocket therebetween in the area of meshing engagement;

a depression formed in the housing adjacent said area and communicating with one of the ports and with the dedendum pocket, said depression having a side wall lying in a plane containing the line of action for said involute gear teeth terminating in an end wall at the plane of the gear axes and thence curving into an opposite side wall defined by a circumferential line spaced radially from the adjacent gear axis, whereby the dedendum pocket is free to the passage of pumped fluid in the connected port.

2. A gear pump comprising;

a housing having an inlet and outlet port;

a pair of meshing gears rotatably received in the housing, the gears each having involute type gear teeth forming alternate adjacent dedendum pockets therebetween in the area of meshing engagement;

a pair of depressions formed in a wall of the housing adjacent said area, each depression lying on opposite sides of a plane through the gear axes, one depression communicating with the inlet port and the other with the outlet port respectively and each communicating with an alternate adjacent dedendum pocket on opposite sides of said plane, said depressions each having a side wall lying in a plane containing to the line of action for said involute gear teeth terminating in an end wall having an extreme end portion lying in the plane of the gear axes and thence curving from said portion into an opposite side wall dened by a circumferential line spaced radially from the adjacent gear axis, whereby uid in one dedendum pocket will escape into the outlet port and fluid will be admitted into the other from the inlet port.

3. A gear pump comprising;

a housing having an inlet and an outlet port;

a pair of meshing gears rotatably received in the housing, the gears each having involute type gear teeth forming alternate adjacent dedendum pockets therebetween in the area of meshing engagement;

a pair of asymmetrical depressions formed in opposed relationship in a wall of the housing adjacent said area, each depression lying on opposite sides of a plane through the gear axes, one depression communicating with the inlet port and the other with the outlet port respectively and each communicating with an alternate adjacent dedendum pocket on opposite sides of said plane, said depressions each having a side wall lying in a plane containing the line of action for said involute type gear teeth terminating in an end wall having an extreme end portion lying in the plane of the gear axes and thence curving from said portion into an opposite side wall defined by a circumferential line spaced radially from the adjacent gear axis at a distance corresponding to the working circle depth thereof, whereby high pressure fluid in one dedendum pocket escapes to the outlet port and low pressure fluid is admitted to the other dedendum pocket from the inlet port.

A gear pump comprising;

a housing having an inlet port and an outlet port each registering with associated interior housing depressions arranged in opposed relationship on opposite sides of a partition separating the depressions centrally of the housing;

a pair of meshing gears rotatably received in the housing each having involute type gear teeth arranged to mesh in the area between the opposed depressions and forming a dedendum pocket in said area cornmunicating rst with the outlet port through its associated depression, and upon gear rotation, with the inlet port through its associated depression without a dead space occurring over said partition, each said depression having a side wall lying in the plane containing the line of action for said involute gear teeth terminating in an end wall defined by said partition and thence curving from said end wall into an opposite side wall defined by a circumferential line spaced radially from the adjacent gear axis at a distance corresponding to the working circle depth thereof, said line of action passing diagonally through said partition without entering any portion of said depressions.

References Cited in the file of this patent UNITED STATES PATENTS 1,129,090 Hawley Feb. 23, 1915 1,719,025 Scheminger July 2, 1929 2,354,992 Gottlieb Aug. 1, 1944 2,833,224 Meyer et al. May 6, 1958 2,884,864 Bobnar May 5, 1959 2,990,783 Oliver July 4, 1961 FOREIGN PATENTS 366,152 Germany Dec. 30, 1922 197,865 Great Britain May 24, 1923 265,511 Great Britain Feb. 10, 1927 

1. A GEAR PUMP COMPRISING; A HOUSING HAVING AN INLET AND AN OUTLET PORT; A PAIR OF MESHING GEARS ROTATABLY RECEIVED IN THE HOUSING, THE GEARS EACH HAVING INVOLUTE GEAR TEETH FORMING A DEDENDUM POCKET THEREBETWEEN IN THE AREA OF MESHING ENGAGEMENT; A DEPRESSION FORMED IN THE HOUSING ADJACENT SAID AREA AND COMMUNICATING WITH ONE OF THE PORTS AND WITH THE DEDENDUM POCKET, SAID DEPRESSION HAVING A SIDE WALL LYING IN A PLANE CONTAINING THE LINE OF ACTION FOR SAID INVOLUTE GEAR TEETH TERMINATING IN AN END WALL AT THE PLANE OF THE GEAR AXES AND THENCE CURVING INTO AN OPPOSITE SIDE WALL DEFINED BY A CIRCUMFERENTIAL LINE SPACED RADIALLY FROM THE ADJACENT GEAR AXIS, WHEREBY THE DEDENDUM POCKET IS FREE TO THE PASSAGE OF PUMPED FLUID IN THE CONNECTED PORT. 